Liposuction evolved from work in the late 1960s from surgeons in Europe using primitive curettage techniques which were largely ignored, as they achieved irregular results with significant morbidity and bleeding. Modern liposuction first burst on the scene in a presentation by the French surgeon, Dr Yves-Gerard Illouz, in 1982. The “Illouz Method” featured a technique of suction-assisted lipolysis after tumesing or infusing fluid into tissues using blunt cannulas and high-vacuum suction and demonstrated both reproducible good results and low morbidity. During the 1980s, many United States surgeons experimented with liposuction, developing variations, and achieving mixed results. Most commonly, liposuction is performed on the abdomen and thighs in women, and the abdomen and flanks in men. According to the American Society for Aesthetic Plastic Surgery, liposuction was the most common plastic surgery procedure performed in 2006 with 403,684 patients.
Traditional liposuction relies on two techniques. The first technique employs a sharp, relatively large diameter (3 mm-5 mm) cannula that is manually manipulated to mechanically break fat down and while applying suction to remove the separated fat. A variation of this vacuum assisted technique is a mechanically powered cannula that reduces the surgeon's fatigue during large surface area liposuction procedures.
The second technique utilizes ultrasonic waves via a vibrating cannula, this technique is mechanical in its nature and significantly reduces the surgeon's fatigue factor. This technique induces the same or worse mechanical trauma to the tissues. Both techniques require significant amounts of fluid, known as a “tumescent solution,” to be injected into the body to emulsify the fat, facilitating the removal of large volumes of fat while reducing blood loss and delivering a local anesthetic (lidocaine) to provide post-operative pain relief. While generally safe, lidocaine can be toxic, leading to serious complications, and even death.
A problem with the probes used in existing liposuction procedures is the generation of significant amounts of heat at the distal tip of the probe, which can exceed the temperature required for melting the fatty tissue. This excess heat can result in burning of tissue, damaging muscles or blood vessels, and even penetrating membranes such as the skin or the peritoneum that covers most of the intra-abdominal organs.
Alternative methods have been disclosed which exploit laser energy to remove unwanted fat. U.S. Pat. Nos. 6,605,080 and 7,060,061 issued to Altshuler, et al. represent an alternative approach in which laser energy is externally applied to the skin to heat and melt fat tissues in epidermis and subcutaneous layers below. These patents disclose the use of near infrared radiation to heat-liquefy fat cells, after which the lipid pool is removed from the subcutaneous area by aspiration. Because of the considerable heat generation that results from the techniques, e.g., up to 70° C., at or in the fat tissue, a special cooling mechanism must be in place to prevent potential temporary skin damage or permanent scarring, with permanent scarring occurring primarily in the dermis. These methods present other limitations and potential adverse thermal effects on tissue above the lipid-rich tissue under treatment, including blistering, peeling, and depigmentation.
U.S. Pat. No. 8,430,919 of Bornstein discloses a lipolysis method in which the skin over the target site is optically irradiated with two different wavelengths of light, one in the near infrared (NIR) region, the other in the infrared range, to modulate biochemical processes of adipocytes in the target site. In order to achieve the desired degree of fat removal, the duration of the treatment must be fairly long, from one to two hours, during which the patient must remain virtually motionless. Unless a sedative or general anesthesia has been administered to calm the patient, physical and psychological discomfort can ensue.
NIR (700-950 nm) is preferable to other types of light for therapeutic use in biological systems because NIR light can pass through blood and tissue to depths of several inches. However, very few organic chromophores absorb in this region, and even fewer are capable of converting the absorbed energy into a chemical or thermal response that can be used to trigger drug release. A few years ago, gold nanostructures (shells, particles, rods, and cages) emerged as useful agents for photothermal therapy after they were shown to have strong absorption in the NIR region (four to five times higher than conventional photo-absorbing dyes) as well as tunable optical resonances. The strong absorption enables effective laser therapy at relatively low laser energies, rendering such therapy methods minimally invasive.
Laser photothermal therapy of cancer with the use of gold nanoparticles immunotargeted to molecular markers has been reported as being effective to selectively kill cancer cells at lower laser powers than those needed to kill healthy cells. (X. Huang, et al., “Determination of the Minimum Temperature Required for Selective Photothermal Destruction of Cancer Cells with the Use of Immunotargeted Gold Nanoparticles”, Photochemistry and Photobiology, 2006, 82:412-417.) Gold nanoparticles absorb light efficiently in the visible region due to coherent oscillations of metal conduction band electrons in strong resonance with visible frequencies of light, a phenomenon known as “surface plasmon resonance” or “SPR”. Photoexcitation of metal nanostructures results in the formation of a heated electron gas that cools rapidly, e.g., within 1 ps, by exchanging energy with the nanoparticle lattice. The nanoparticle lattice, in turn, rapidly exchanges energy with the surrounding medium on the timescale of 100 ps, causing localized heating. This rapid energy conversion and dissipation can be achieved by using light radiation with a frequency that strongly overlaps the nanoparticle absorption band. Nanorods exhibit cylindrical symmetry, and simple changes in particle symmetry can significantly alter SPR characteristics. The NIR absorption maximum of metal nanostructures can be modulated by changing their size, shape and aggregation. GNRs have two plasmon absorption peaks, exhibiting transverse and longitudinal surface plasmon resonances that correspond to electron oscillations perpendicular and parallel to the rod length direction, respectively. The longitudinal surface plasmon wavelengths are tunable from the visible to infrared regions. The effectiveness of GNRs as photothermal therapeutic agents is strongly dependent on their scattering and absorption cross-sections—large absorption cross sections with small scattering losses allow for photothermal therapy with a minimal laser dosage. In addition, the longitudinal surface plasmon wavelengths of GNRs are preferably within the spectral range of 650-900 nm. Light irradiation in this region can penetrate more deeply into tissues and cause less photodamage than UV-visible irradiation. Therefore, the ability to tailor both scattering and absorption of GNRs with different longitudinal surface plasmon wavelengths is important for therapeutic applications.